All trading is officially done during trade week (spans from the Monday week after the AFL Grand Final to the Friday of the same week).
What can be traded:
> Any player including rookie listed player and first year players in contract – provided there is an agreement between the player and his current club
> Current national draft picks
What can’t be traded:
> Pre-season or Rookie draft picks
> Players that don’t agree to be traded
Clubs are able to trade picks without a player being involved e.g. in 2007 West Coast traded picks 30 and 35 to the Western Bulldogs for pick 22.
All clubs must have a full list of 38 players contracted (players on the veterans list and rookie list are excluded from this total). These players are eligible to play in any AFL game.
A player may be put on the veterans list if they are over the age of 30 and have played for 10 seasons at the club. A club may list upto 2 veterans – any additional nominated veterans will remain on the main list. When a player is moved to the veterans list he can’t be returned to the main list unless he is delisted and re-drafted by the club.
Nominated veterans (both on the main and veterans list) allow clubs salary cap relief to the amount of:
1 nominated veterans – 50% reduction each
2 nominated veterans - 50% reduction each
3 nominated veterans - 33% reduction each
4 nominated veterans – 25% reduction each
Clubs may list upto 8 rookies minus the number of players on the veterans list (i.e. 1 player on the veterans list = maximum 7 rookies allowed, 2 players on the veterans list = maximum 6 rookies allowed). Rookie players aren’t eligible to play in AFL games unless they are elevated to the senior list (replacing a retiree, long term injured main listed player or as one of upto 2 ‘nominated’ rookies minus the number of veteran listed players – i.e. 0 veteran listers = 2 nominated rookies allowed, 1 veteran lister = 1 nominated rookie allowed, 2 veteran listers = 0 nominated rookies allowed).
Rookies can be retained for 2 years and may be redrafted to the same club till no longer eligible to rookie listed. Any rookie that reaches 23 during a season, must be delisted at the end of that season (unless they are a mature aged rookie).
A club may also list one player who hasn’t played at AFL level (they are allowed to have previously been on an AFL list), over the age of 23 as a mature aged rookie amongst the 6-8 rookie spots available.
Derived from: http://www.eaglesflyinghigh.com/forum/viewtopic.php?f=10&t=10956